Brake Horsepower Calculator
What a Dyno Actually Measures
"Brake horsepower" gets its name from the Prony brake, an early dynamometer that measured engine output by applying a mechanical braking force and recording how hard the engine had to work against it. Modern engine dynos still measure the same thing: power delivered at the crankshaft or flywheel, before it passes through the clutch, gearbox, differential, and driveshafts on its way to the wheels. That distinction matters — a horsepower figure quoted by a manufacturer is almost always this crank-measured BHP figure, not the lower number a chassis dyno would read at the wheels.
The Formula
Metric: kW = (Torque[Nm] × RPM) ÷ 9550, then BHP = kW × 1.34102
Both versions require torque measured directly at the engine — on an engine dyno or from a manufacturer's published crank-torque curve — rather than torque measured at the wheels.
Where This Matters
- Comparing manufacturer specs — published horsepower ratings are BHP figures measured under standardized dyno conditions, making them directly comparable across engines when torque and RPM are known.
- Engine building and tuning — engine builders track BHP through a build because it isolates the engine itself from whatever drivetrain it will eventually sit behind.
- Understanding wheel horsepower differences — a chassis dyno reading is always lower than BHP because of drivetrain friction; rear-wheel-drive drivetrains are commonly cited as losing somewhere in the range of 15–20% of crank power, all-wheel-drive typically more.
- Verifying aftermarket claims — converting a claimed torque figure and RPM into BHP is a quick sanity check against a stated horsepower number.
BHP at 400 Nm Constant Torque
| RPM | Power (kW) | Brake Horsepower |
|---|---|---|
| 1,500 | 62.8 kW | 84.3 BHP |
| 2,500 | 104.7 kW | 140.4 BHP |
| 3,500 | 146.6 kW | 196.6 BHP |
| 4,500 | 188.5 kW | 252.8 BHP |
| 5,500 | 230.4 kW | 308.9 BHP |
| 6,500 | 272.3 kW | 365.1 BHP |
Computed from kW = (Torque × RPM) ÷ 9550, then BHP = kW × 1.34102, at a constant 400 Nm.
How to Use This Calculator
- Select Imperial (lb-ft) or Metric (Nm) for the torque units.
- Enter the torque value, as measured on a dyno at the crankshaft or flywheel.
- Enter the RPM at which that torque was recorded.
- Select Calculate to see the equivalent brake horsepower.
Related Calculations
To estimate horsepower loss to the drivetrain, compare against the Horsepower Calculator, or work the calculation in reverse with the Torque Calculator.